Method for installing metal piles in permafrost soil

ABSTRACT

A method for installing driven cast-in-situ supports of pipes, power transmission towers, and in the mounting of buildings and structures on permafrost soils excludes the ingress of slurry and groundwater into the hole when installing driven cast-in-situ piles in permafrost soils in summer having a thawed seasonal freezing and thawing layer while avoiding the impact of frost heaving forces of soil from seasonal freezing conditions. The method includes driving a casing pipe at a depth of seasonal freezing and thawing of soil, drilling a pilot hole at a depth of not less than the depth of seasonal freezing and thawing of the soil, pouring hardening material in the amount required to fill in the space between the pilot hole walls and the pile from the bottom of the pilot hole to the bottom of seasonal freezing and thawing soil layer, installation of the pile in the pilot hole and poured mortar, and filling the remaining space between the pile and the casing pipe with non-frost heaving loose inert material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit and priority of PCT Pat. App. No. PCT/RU2014/000211, titled METHOD FOR INSTALLING METAL PILES IN PERMAFROST SOIL filed on Mar. 28, 2014, also published as WO/2015/147676.

FIELD

The present disclosure relates to the field of construction, particularly to welding of above- and underground pipelines an ultimate tensile strength in the range of 590-690 MPa.

BACKGROUND

It is known that there are methods for manufacturing in situ piles, comprising the following basic operations: arrangement of the well and pouring hardening material, i.e. ready-mix concrete (Foundations, bases and tests of facilities, M. I. Garbunov-Pasadov, V. A. Ilyichev, Yu. G. Trofimenkova.—Moscow, Stroyizdat, 1985.—480 pages, illustrated—(Designer's Handbook), p. 159). However, this method does not preclude the ingress of slurry and groundwater in the hole prior to pouring of the concrete.

It is also known an arrangement of driven cast-in-situ piles in all conditions wherein temperature of the ground is below −0.5° C. First, holes with a diameter 5-10 cm greater than the transverse dimension of the pile are drilled in the foundation. Then the holes are filled with soil mortar, and the piles are installed. After the mortar has been frozen, the pile is securely clamped in the permafrost soil (Soil mechanics, bases and foundations, S. B. Ukhov, V. V. Semenov, V. V. Znamensky, Z. G. Ter-Martirosyan, S. N. Chernyshev, ASV Publishing House, 1994—p. 405). A disadvantage of this method for fabricating the driven cast-in-situ piles is non-preclusion of the impact of frost heaving forces of soil, resulting from the heaving deformations in seasonal freezing conditions. Also, this method does not exclude the ingress of slurry and groundwater into the hole when arranging driven cast-in-situ piles in permafrost soils in the summer in soils having a seasonal freezing and thawing layer that contains liquid (thawed) water.

Another known method is directed to construction of piles in mollisol heaving soils. The method consists of drilling a pilot hole and installing the pile into the hole. The pilot hole is drilled to a depth of not less than standard depth of soil freezing, and the pilot hole diameter is selected on the basis of this relation. Then, a space formed by the pilot hole is filled with non-frost heaving loose inert material up to the mouth of the pilot hole, after which a pile is installed in its center at a target depth (patent RU No. 2474652, published on Feb. 10, 2013, IPC E02D5/50). However, during manufacturing the piles in permafrost soils in the summer with watered soils of seasonal freezing layer, this technology does not eliminate the problem of ingress of slurry and groundwater into the hole when installing driven cast-in-situ piles, that entails sludging-up and watering of the hole, and as a consequence, reduction in the bearing capacity of the driven cast-in-situ pile due to the failure to feed the required full amount of cement and sand mortar to fill the space between the pile and the hole.

It would be desirable, therefore, to overcome the drawbacks of these methods while retaining their advantages, by developing a new method for installing piles in permafrost soils during summertime when the seasonal freezing and thawing layer over the permafrost is thawed.

SUMMARY

Objects of the technology of piles installation disclosed herein include preventing an ingress of slurry and groundwater into the hole when arranging driven cast-in-situ piles in permafrost soils in summer in soils having a thawed seasonal freezing and thawing layer, and avoiding the impact of frost heaving forces of soil resulting from the heaving deformations in seasonal freezing conditions.

The technical result consists in compliance with appropriate quality of works in the installation of driven cast-in-situ piles in permafrost soils in summer in soils having a thawed seasonal freezing and thawing layer in order to exclude the reduction in the bearing capacity of driven cast-in-situ piles with the ingress of slurry and groundwater into the hole, and avoid the impact of frost heaving forces of soil, resulting from the heaving deformations in seasonal freezing conditions.

The technology for meeting the desired objects includes a method of installation of metal piles, which includes drilling of a pilot hole, installing a pipe metal pile and pouring non-frost heaving loose inert material. According to the technology, a casing pipe is driven to a depth of seasonal soil freezing and thawing before drilling a pilot hole. Then, the method includes drilling the pilot hole to a depth of not less than standard depth of freezing soil, pouring hardening material in the amount needed for filling space between the pilot hole and the pile from the bottom of the pilot hole to the bottom of seasonal freezing and thawing soil layer, installing the pile in the hardening material and filling space between the pile and the casing pipe with non-frost heaving loose inert material.

The chosen diameter of the casing pipe is 10-20 cm greater than that of the pile. The optimal installation depth for the casing pipe is the depth of seasonal freezing and thawing of soil plus 0.5-1 m.

Diameter of the pilot hole is 5-15 cm greater than the pile diameter, and the depth is up to 30 meters. M10-M100 mortar may be used as cement and sand mortar.

Non-frost heaving coarse sand and medium coarse sand is used as non-frost heaving loose inert material.

The volume of cement and sand mortar is previously calculated by the following formula:

V=πR ₁ ² *l ₁ −πR ₂ ² *l ₂,

where R₁ is the radius of the pilot hole, l₁ is the length of the pilot hole; R₂ is the radius of the pile, l₂ is the length of the pile, and π is pi.

The time between pouring of cement and sand mortar and installation of the pile should not exceed 15 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings.

FIG. 1 is a schematic diagram illustrating the pile with the casing.

DETAILED DESCRIPTION

Various aspects are now described with reference to FIG. 1, wherein the following components are illustrated: 1—pile, 2—casing pipe, 3—filler—hardening material, such as cement and sand mortar, 4—filler—non-frost heaving loose inert material, 5—pilot hole, 6—casing pipe interior space.

An embodiment is implemented as follows. The casing pipe 2 is driven in the soil to a depth below seasonal freezing and thawing of the soil, for example 1.8-3 m, using a pile-driving engine with diesel or pneumatic hammer. This technology of installation of the casing pipe excludes the reduction in the bearing capacity of driven cast-in-situ piles when slurry or groundwater penetrates into the hole while working in permafrost soils in summer having a thawed seasonal freezing and thawing layer. This is followed by the drilling of a pilot hole at a depth equal to the depth of installation of the pile, then the auger of the drilling machine is removed and the entire soil is drilled out from the interior of the casing pipe 6 to below the depth of seasonal freezing of soil, e.g., 1.8-3 m. After removing the auger, cement and sand mortar 3 is poured in the hole in an amount calculated to fill in the space between the pilot hole 5 and the pipe metal pile 1 from the bottom of the pilot hole up to the bottom of the seasonal freezing and thawing soil layer (i.e., to the upper limit of the permafrost layer). Upon completion of pouring the mortar, the pipe pile 1 is installed up to a design mark that indicates immersion to the bottom of the pilot hole, using a vibro-driver. After installing the pile 1, remaining space 6 between the pile 1 and the casing pipe 2 are filled with non-frost heaving loose inert material 4 to a depth of 1.8-3 m to the top of the casing pipe 2 in order to exclude the impact of frost heaving forces arising from the deformation of heaving in seasonal freezing and thawing conditions.

More detailed examples of the embodiment follows. The casing pipe 3 with a diameter ‘d’ in a range of 720 to 820 mm and wall thickness t in a range of 9 to 12 mm, 1.8 to 3 m long and made of 17G1 S, 17G1S-U, St2kp, St2ps, St2sp, St3kp, St3ps, St3sp, St3ps3, St3sp3, St3ps4, St3sp40, or 9G2S steel grade, and K34-K60 strength class is driven into the soil to a depth below seasonal freezing and thawing of soils, equal to 1.8 to 3 m. The pilot hole 5 should have a diameter of ‘d’ in a range of 480-500 mm and depth in a range of 6 to 20 m. The soil of the interior 6 of the casing pipe 2 is removed, for example by being drilled out using an auger having a diameter in a range of 680 to 780 mm. The pile 1 is made of pipe metal-roll with a diameter equal to 426 mm, wall thickness 10-12 mm and a length in a range of 6 to 20 m long, made of 17G1S, 17G1S-U, St2kp, St2ps, St2sp, St3kp, St3ps, St3sp, St3ps3, St3sp3, St3ps4, St3sp40, or 9G2S steel grade, K34-K60 strength class. The pile serves to accommodate vertical, horizontal and other loads. Before installing the pile 1 in the pilot hole 5, the pilot hole 5 is filled with cement and sand mortar 3 in a range of M75-M150 grade in the amount necessary to fill in the space between the pilot hole 5 and the pile 1 from the bottom of the pilot hole to the bottom of the seasonal freezing and thawing soil layer. After installing the pile 1 in the pilot hole 5, the space between the casing pipe 2 and the pile 1 is filled with non-frost heaving loose inert material 4.

Non-frost heaving coarse sand and medium coarse sand is used as non-frost heaving loose inert material.

The volume of cement and sand mortar may be calculated before pouring of mortar by the following formula:

V=πR ₁ ² *l ₁ −πR ₂ ² *l ₂,

where R₁ is the radius of the pilot hole, l₁ is the length of the pilot hole below the permafrost line; R₂ is the radius of the pile, l₂ is the length of the pile below the permafrost line, and π is pi.

The time between pouring of cement and sand mortar and installation of the pile should not exceed 15 minutes.

Using this method of arrangement of driven cast-in-situ piles with the casing pipe in permafrost soils in summer with thawed, water-containing soils of a seasonal freezing and thawing layer prevents reduction in bearing capacity of driven cast-in-situ piles with the ingress of slurry and groundwater in the hole, avoiding the impact of frost heaving forces resulting from heaving deformations in seasonal freezing and thawing conditions. 

1. A method for installing piles in permafrost soils, comprising: driving a casing pipe into soil to a depth of not less than a depth limit of seasonal freezing and thawing of the soil; drilling a pilot hole to a depth of not less than the depth limit; removing soil from an interior of the casing pipe; pouring into the pilot hole an amount of cement and sand mortar that fills in space between walls of the pilot hole and the pile from a bottom of the pilot hole up to a bottom of a seasonal freezing and thawing soil layer; installing a pile in the pilot hole with the cement and sand mortar; and filling space between the pile and the casing pipe with non-frost heaving loose inert material.
 2. The method of claim 1, wherein the cement and sand mortar is in a range of M10 to M100.
 3. The method of claim 1, wherein the cement and sand mortar is in a range of M75 to M150.
 4. The method of claim 1, wherein the non-frost heaving loose inert material comprises at least one of coarse sand or medium sand.
 5. The method of claim 1, further compromising calculating a volume of the amount of cement and sand mortar by πR₁ ²*l₁−πR₂ ²*l₂, where R₁ is the radius of the pilot hole, l₁ is the length of the pilot hole; R₂ is the radius of the pile, l₂ is the length of the pile, and π is pi.
 6. The method of claim 1, wherein time between the pouring of cement and sand mortar and the installing of the pile does not exceed 15 minutes.
 7. The method of claim 1, wherein the casing pipe has a diameter that in greater than a diameter of the metal pile by an amount in a range of 10 to 20 cm.
 8. The method of claim 1, wherein the pilot hole has a diameter that is greater than a diameter of the metal pile by an amount in a range of 10-20 cm.
 9. The method of claim 1, wherein driving a casing pipe comprises driving the casing pipe to the depth in a range of 1.8 to 3 meters.
 10. The method of claim 1, wherein the casing pipe has a diameter in a range of 720 to 820 mm, a wall thickness in a range of 9 to 12 mm, and a length in a range of 1.8 to 3 meters.
 11. The method of claim 10, wherein the casing pipe is made of a material selected from: 17G1S, 17G1S-U, St2kp, St2ps, St2sp, St3kp, St3ps, St3sp, St3ps3, St3sp3, St3ps4, St3sp40, or 9G2S steel.
 12. The method of claim 1, wherein the pilot hole has a diameter in a range of 480 to 500 mm.
 13. The method of claim 12, wherein the pilot hole has a depth in a range of 6 to 20 meters.
 14. The method of claim 13, wherein the metal pile has a diameter of 426 mm.
 15. The method of claim 13, wherein the metal pile has a wall thickness in a range of 10 to 12 mm and a length in a range of 6 to 20 meters.
 16. The method of claim 15, wherein the metal pile is made of a material selected from: 17G1S, 17G1S-U, St2kp, St2ps, St2sp, St3kp, St3ps, St3sp, St3ps3, St3sp3, St3ps4, St3sp40, or 9G2S steel.
 17. The method of claim 1, wherein the removing soil comprises auguring.
 18. The method of claim 17, wherein the auguring is performed using an augur having a diameter in a range of 680 to 780 mm. 